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LGA 771 Socket Mechanical Design Guide 7
Introduction
1 Introduction
1.1 Document Goals and Scope
1.1.1 LGA771 Socket Overview
This document describes a surface mount, LGA (Land Grid Array) socket intended for
the Dual-Core Intel
®
Xeon
®
Processor 5000 Sequence Family for Servers and
Workstations. The socket provides I/O, power and ground contacts. The socket
contains 771 contacts arrayed about a cavity in the center of the socket with solder
balls for surface mounting with the motherboard. The LF-LGA771 Socket contains lead-
free solder balls while the LGA771 Socket contains eutectic solder balls. This Design
Guide will refer to the socket as LGA771 for simplicity, but its contents are applicable to
both lead-free and eutectic solder materials unless otherwise specified. The socket
contacts have 1.09 mm X 1.17 mm pitch (X by Y) in a 33x30 grid array with 15x14 grid
depopulation in the center of the array and selective depopulation for keying features.
A matching LGA package will be mated with the socket.
For board layout, the land pattern for the LGA771 socket is 43 mils X 46 mils (X by Y),
and the pad size is 18 mils. The component dimensions are defined in metric so there is
a slight round-off error when converting to mils, but it is a negligible amount, relatively
speaking, when compared to the size of the ball and pad. There have been no reported
manufacturing issues.
1.1.2 Document Goals
The goals of this document are:
• To provide LGA771 socket information necessary for motherboard design to ensure
the specified performance of the platform.
• To define the boundary conditions and design constraints within which the socket
design must fit and perform.
1.1.3 Important Remarks
All LGA771 socket characteristics mentioned in this document may change.
LGA771 socket validation reports are available from socket vendors.